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  • 1
    Book
    Book
    Ground-truth observations of ice-covered North Slope lakes imaged by radar (1981)
    Hanover, NH : U.S. Army Cold Regions Research and Engineering Laboratory
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    UID:
    kobvindex_GFZ20210323141617
    Format: iii, 17 Seiten , Illustrationen
    Series Statement: CRREL Report 81-19
    Content: Field observations support the interpretation that differences in the strength of radar returns from the ice covers of lakes on the North Slope of Alaska can be used to determine where the lake is frozen completely to the bottom. An ice/frozen soil interface is indicated by a weak return and an ice/ water interface by a strong return. The immediate value of this result is that SLAR (side-looking airborne radar) imagery can now be used to prepare maps of large areas of the North Slope showing where the lakes are shallower or deeper than 1.7m (the approximate draft of the lake ice at the time of the SLAR flights). The bathymetry of these shallow lakes is largely unknown and is not obvious from their sizes or outlines. Such information could be very useful, for example in finding suitable year-round water supplies.
    Note: CONTENTS Abstract Preface Introduction The experiment Results Maps of completely frozen North Slope lakes Literature cited
    In: CRREL Report, 81-19
    Language: English
    Keywords: Forschungsbericht
    URL: https://hdl.handle.net/11681/9424
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  • 2
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    Some elements of iceberg technology (1978)
    Hanover, NH : U.S. Army Cold Regions Research and Engineering Laboratory
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    UID:
    kobvindex_GFZ106220
    Format: v, 31 Seiten , Illustrationen
    Series Statement: CRREL Report 78-2
    Content: Many of the technical questions relating to iceberg transport are given brief, but quantitative, consideration. These include iceberg genesis and properties, the mechanical stability of icebergs at sea, towing forces and tug characteristics, drag coefficients, ablation rates, and handling and processing the iceberg at both the pick-up site and at the final destination. In particular the paper attempts to make technical information on glaciological and ice engineering aspects of the problem more readily available to the interested planner or engineer. Specific conclusions include: (1) No unprotected iceberg, no matter how long or wide, would be likely to survive the ablation caused by a long trip to low latitudes. (2) Icebergs that have a horizontal dimension exceeding 2 km may well be prone to breakup by long wavelength swells. (3) To avoid the dangers associated with an iceberg capsizing, the width of a 200-m thick iceberg should always be more than 300 m. (4) For towing efficiency the length/width ratio of a towed iceberg should be appreciably greater than unity. (5) For a pilot project, the selected iceberg would have to be quite small, if for no other reason than the practical availability of tug power.
    Note: MAB0014.001: ZSP-201-78/2 , CONTENTS Abstract Preface Introduction Sources and properties of tabular icebergs Sources Characteristics of ice shelves near the ice front Characteristics of tabular icebergs Towing Geophysical and engineering considerations Tug characteristics Handling and processing Cutting and boring with thermal devices Penetration with electrothermal devices Electrothermal cutting Making vertical cuts by pre-split blasting Primary fragmentation by blasting Primary fragmentation by mechanical sawing Comminuting ice with machines Slurry pipelines Conclusion Literature cited
    In: CRREL Report, 78-2
    Language: English
    Keywords: Forschungsbericht
    URL: https://hdl.handle.net/11681/9421
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  • 3
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    Thickness and roughness variations of Arctic multiyear sea ice (1976)
    Hanover, NH : U.S. Army Cold Regions Research and Engineering Laboratory
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    UID:
    kobvindex_GFZ107373
    Format: v, 25 Seiten , Illustrationen
    Series Statement: CRREL Report 76-18
    Content: Three surface elevation and ice thickness profiles obtained during the 1972 Arctic Ice Dynamics Joint Experiment on a multiyear ice floe were analyzed to obtain relationships between surface elevation, thickness and physical properties of the ice. It was found that for ice freeboards from 0.10 m to 1.05 m above sea level a linear relationship between ice density and freeboard could be postulated. The equation for the regression line is: Ice density = -194f' + 974 kg/cu m where f' is the ice freeboard plus snow depth in ice equivalent at the point in question. This statistical relationship is consistent with observed physical properties, which indicate that as the ice freeboard increases, ice salinity decreases and the higher freeboard or thicker ice therefore decreases in density. Using this variable density with freeboard relationship, a model was constructed to predict ice thickness, given ice freeboard and snow depth alone. This prediction is desirable, since snow depth and freeboard are relatively easy to obtain, whereas ice thickness can usually be obtained only by drilling through the ice. The model was compared with two other models. It was found that the variable density prediction model gave the best approximation to observed ice thickness, with a standard error between the measured and predicted value of about 0.4 m, compared with errors from 50 to 100% higher for the other two models.
    Note: MAB0014.001: ZSP-201-76/18 , Contents Abstract Preface Summary Introduction Previous work Results Models for predicting thickness from ice freeboard Comparison between measured and predicted thicknesses Spectral behavior of measured and predicted profiles Comparisons of ice thickness using airborne laser profilometry Conclusions Literature cited Appendix A: Misgivings on isostatic imbalance as a mechanism for sea ice cracking
    In: CRREL Report, 76-18
    Language: English
    Keywords: Forschungsbericht
    URL: Abstract
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  • 4
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    Book
    Brine drainage and initial salt entrapment in sodium chloride ice (1975)
    Hanover, NH : U.S. Army Cold Regions Research and Engineering Laboratory
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    UID:
    kobvindex_GFZ122933
    Format: vii, 85 Seiten , Illustrationen
    Series Statement: Research report / Cold Regions Research and Engineering Laboratory 345
    Content: CONTENTS: Abstract. - Preface. - List of symbols. - Introduction. - Previous work. - Experimental design. - The radioisotope 22Na. - Description of apparatus. - Experimental procedure. - Correction of profiles. - Assumptions. - Decay correction. - Boundary correction. - Error analysis. - Results. - Salinity data. - Temperature data. - Growth velocity. - Discussion. - Brine and ice properties. - Brine salinity. - Brine density. - Brine volume. - Brine latent heat of freezing. - Brine viscosity, specific heat, and thermal conductivity. - Ice properties. - Theoretical brine expulsion model. - Continuity equations. - Thermal energy equation. - Simplified brine expulsion equations. - Brine expulsion in NaCl ice. - Results. - Discussion. - Gravity drainage in NaCl ice. - Application of results to natural sea ice. - Effective distribution coefficient. - Previous work. - Experimental procedure and results. - Conclusions. - Literature cited. - Appendix A: Profile correction data. - Appendix B: Program "correct" and sample output. - Appendix C: Tabulation of salinity data. - Appendix D: Tabulation of profile data. - Appendix E: Time-ice thickness equations (Runs 2 and 3). - Appendix F: Tabulation of distribution coefficient data.
    Content: To obtain a better understanding of the desalination of natural sea ice, an experimental technique was developed to measure sequential salinity profiles of a growing sodium chloride ice sheet. Using radioactive 22Na as a tracer, it was possible to determine both the concentration and movement of the brine within the ice without destroying the sample. A detailed temperature and growth history of the ice was also maintained so that the variation of the salinity profiles could be properly interpreted. Since the experimental salinity profile represented a smoothed, rather than a true salinity distribution, a deconvolution method was devised to restore the true salinity profile. This was achieved without any significant loss of end points. In all respects, the salinity profiles are similar to those of natural sea ice. They have a characteristic C-shape, and clearly exhibit the effects of brine drainage. Not knowing the rates of brine expulsion or gravity drainage, the variation of the salinity profiles during the period of ice growth could be explained by either process. To determine the relative importance of the desalination mechanisms, a theoretical brine expulsion model was derived and compared to the experimental data. As input for the model, equations describing the variation of some properties of NaCl brine with temperature were derived. These included the brine salinity, viscosity, specific heat, thermal conductivity, and latent heat of freezing. The theoretical brine expulsion model was derived by performing mass and energy balances over a control volume of NaCl ice. A simplified form of the model, when compared to the experimental results, indicated that brine expulsion was only important during the first several hours of ice growth, and later became a minor desalination process relative to gravity drainage which continued to be the dominant mechanism for the remainder of the study period (up to 6 weeks). The rate of gravity drainage was found to be dependent on the brine volume and the temperature gradient of the ice. As either the brine volume or temperature gradient was increased, the rate of change of salinity due to gravity drainage increased. The equation commonly used to calculate the effective distribution coefficient (Weeks and Lofgren 1967) was modified and improved by taking brine drainage into account. An expression was also derived to give the distribution coefficient at very low growth velocities.
    Note: MAB0014.001: ZSP-202-345
    In: Research report / Cold Regions Research and Engineering Laboratory, 345
    Language: English
    Keywords: Forschungsbericht
    URL: https://apps.dtic.mil/docs/citations/ADA021765
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  • 5
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    Book
    Sea ice ridging over the Alaskan continental shelf (1979)
    Hanover, NH : U.S. Army Cold Regions Research and Engineering Laboratory
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    UID:
    kobvindex_GFZ105552
    Format: iv, 28 Seiten , Illustrationen
    Series Statement: CRREL Report 79-8
    Content: Sea ice ridging statistics obtained from a series of laser surface roughnessprofiles are examined. Each set of profiles consists of six 200-km-long flight tracks oriented approximately perpendicular to the coastline of the Chukchi and Beaufort Seas. The landward ends of the profiles were located at Point Lay, Wainwright, Barrow, Lonely, Cross Island and Barter Island. The flights were made in February, April, August, and December 1976, and one additional profile was obtained north of Cross Island during March 1978. It was found that although there is a systematic variation in mean ridge height (h) with season (with the highest values occurring in late winter), there is no systematic spatial variation in h at a given time. The number of ridges/km (micron) is also high during the late winter, with the highest values occurring in the Barter and Cross Island profiles . In most profiles, the ice 20 to 60 km from the coast is more highly deformed (higher micron values) than the ice either nearer the coast or farther seaward. The Wadhams model for the distribution of ridge heights gives better agreement with observed values in the higher ridge categories than does the Hibler model. Estimates of the spatial recurrence frequency of large pressure ridges are made by using the Wadhams model and also by using an extreme value approach. In the latter, the distribution of the lagest ridges per 20 km of laser track was found to be essentially normal
    Note: MAB0014.001: ZSP-201-79/8 , CONTENTS Abstract Preface Introduction Data collection and processing Analysis General Variations in ridging Ridge height distributions Occurrence of high ridges The tail of the distribution Extreme values Applications to offshore design Conclusions Literature cited Appendix A. Tabulated ice ridge data
    In: CRREL Report, 79-8
    Language: English
    Keywords: Forschungsbericht
    URL: https://hdl.handle.net/11681/9015
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  • 6
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    Book
    Differential sea ice drift (1975)
    Hanover, NH : Corps of Engineers, U.S. Army, Cold Regions Research and Engineering Laboratory,
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    UID:
    kobvindex_GFZ122977
    Format: v, 37 Seiten , Illustrationen
    Series Statement: Research report / Cold Regions Research and Engineering Laboratory, CRREL, US Army Material Command 329
    Content: CONTENTS: General Introduction. - Part I. Spatial and temporal variations in sea ice deformatfon. - Introduction. - Approach. - Site location and data collection procedures. - Data analysis. - Strain results. - Comparison of mesoscale deformation with macroscale deformation. - Nature of the ice pack rotation. - Conciusion. - Literature cited. - Part Il. Comparison of mesoscale strain measurements with linear drift theory predictions. - Introduction. - List of symbols. - Linear drift equations. - Ice drift solutions. - Comparison of theory with mesoscale measurements. - A more general linear constitutive law. - Conclusions. - Literature cited. - Appendix Relative magnitudes of differential drift forces. - Abstract.
    Content: Measurements of mesoscale sea ice deformation over a region approximately 20 km in diameter were made over a five-week period in the spring of 1972 at the main AIDJEX camp in the Beaufort Sea. They have been analyzed to determine nonlinearities in the ice velocity field (due to the discrete small-scale nature of the ice pack), as well as a continuum mode of deformation represented by a least squares strain rate tensor and vorticity. The deformation rate time series between Julian day 88 and 113 exhibited net areal changes as large as 3% and deformation rates up to 0.16% per hour. In the principal axis coordinate system, the strain rate typically exhibited a much larger compression (or extension) along one axis than along the other. Persistent cycles at ~12-hour wavelengths were observed in the divergence rate. A comparison of the average residual error with the average strain rate magnitude indicated that strains measured on a scale of 10 km or greater can serve as a valid measure of the continuum motion of the sea ice. This conclusion is also substantiated by a comparison between the mesoscale deformation, and macroscale deformation measured over a ~100-km-diameter region. Vorticity calculations indicate that at low temporal frequencies ( 〈 0.04 hr^-1 ) the whole mesoscale array rotates essentially as an entity and consequently the low frequency vorticity can accurately be estimated from the rotation of a single floe. (Part I) A comparison of mesoscale strain measurements with the atmospheric pressure field and the wind velocity field indicated that the ice divergence rate and vorticity followed the local pressure and wind divergence with significant correlation. For low atmospheric pressures and converging winds, the divergence rate was negative with the vorticity being counterclockwise. The inverse behavior was observed for high pressures and diverging winds. This behavior agreed with predictions based upon the infinite boundary solution of a linearized drift theory in the absence of gradient current effects and using the constitutive law proposed by Glen for pack ice. The best least squares values of the constitutive law parameters [Eta] and [Zeta] were found to be given by ~10^12 kg sec^-1. Using typical divergence rates, these values yielded compressive stresses of the magnitude of 10^5 N m^-1, which are similar to values suggested by the Parmerter and Coon ridge model. In general, the infinite boundary solution of the linear drift equation indicates that in a low pressure region that is reasonably localized in space, the ice would be expected to converge for high compactness (winter) and diverge for low compactness (summer). Calculations were also carried out using a more general linear viscoelastic constitutive law that includes memory effects and that includes a generalized Hooke's law as well as the Glen law as special cases. A best fit of this more general calculation with strain measurements indicates, overall, a better agreement with viscous behavior than with elastic behavior, with the frequency behavior of the estimated "viscosities" similar to the Glen law behavior at temporal frequencies less than ~0.01 hr^-1 (Part II)
    Note: MAB0014.001: ZSP-202-329 , Online frei verfügbar
    In: Research report
    Language: English
    Keywords: Forschungsbericht
    URL: http://www.worldcat.org/oclc/1387886
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  • 7
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    Book
    Statistical aspects of ice gouging on the Alaskan Shelf of the Beaufort Sea (1983)
    Hanover, NH : U.S. Army Cold Regions Research and Engineering Laboratory
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    UID:
    kobvindex_GFZ20190618133333
    Format: 40 Seiten , Illustrationen, 1 Karte
    Series Statement: CRREL Report 83-21
    Content: The probability density function of the gouge depths into the sediment is represented by a simple negative exponential over four decades of gouge frequency. The exceedance probability function is, therefore, e to the -lambda d, where d is the gouge depth in meters and lambda is a constant. The value of lambda shows a general decrease with increasing water depth, from 9/m in shallow water to less than 3/m in water 30 to 35 m deep. The deepest gouge observed was 3.6 m, from a sample of 20,354 gouges that have depths greater than or equal to 0.2 m. The dominant gouge orientations are usually unimodal and reasonably clustered, with the most frequent alignments roughly parallel to the general trend to the coastline. The value of N(bar) sub 1, the mean number of gouges (deeper than 0.2 m) per kilometer measured normal to the trend of the gouges, varies from 0.2 for protected lagoons to 80 in water between 20 and 38 m deep in unprotected offshore regions. The distribution of the spacings between gouges as measured along a sampling track is a negative exponential. The form of the frequency distribution of N sub 1 varies with water depth and is exponential for lagoons and shallow offshore areas, previously skewed for 10 to 20 m depths off the barrier islands, and near-normal for deeper water. As a Poisson distribution gives a reasonable fit to the N sub 1 distributions for all water depths, it is suggested that gouging can be taken as approximating a Poisson process in both space and time. The distributions of the largest values per kilometer of gouge depths, gouge widths, and the heights of the lateral embankment of sediments plowed from the gouges are also investigated.
    Note: CONTENTS Abstract Preface Introduction Background and environmental setting Data collection and terminology Data analysis Gouge depths Gouge orientation Gouge frequency Extreme value analysis Applications to offshore design Gouge depth Extreme value statistics Burial depths Conclusion Literature cited Appendix A: Detailed bathymetric map of the Alaskan portion of the Beaufort Sea
    In: CRREL Report, 83-21
    Language: English
    Keywords: Forschungsbericht
    URL: https://apps.dtic.mil/docs/citations/ADA134428
    URL: https://hdl.handle.net/11681/9302
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  • 8
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    Variation of some mechanical properties of polar snow, Camp Century, Greenland (1969)
    Hanover, NH : U.S. Army Corps of Engineers, Cold Regions Research and Engineering Laboratory
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    UID:
    kobvindex_GFZ123540
    Format: 35 Seiten , Illustrationen, graphische Darstellungen
    Series Statement: Research report / Cold Regions Research and Engineering Laboratory, CRREL, US Army Material Command 276
    Content: CONTENTS: Introduction. - Test site. - Test procedures. - Equipment. - Unconfined compression tests. - Ring tensile tests. - Test results. - Unconfined compression tests. - Ring tensile tests. - Discussion. - Literature cited. - Appendix A. Calculation of the effect of nonaxial loading of unconfined compression specimens. - Appendix B. Camp Century unconfined compressive strength data at -25C. - Appendix C. Camp Century ring-tensile strength data at -25C. - Appendix D. Unconfined compressive strength of Camp Century vertical snow samples 8.25 in. length, 3.0 in. diam at -25C. - Abstract.
    Content: The unconfined compressive strengths [Sigma]c and the ring-tensile strengths [Sigma]T of snow and ice specimens from the Inclined Drift at Camp Century, Greenland, were determined. The specimen densities varied over essentially the complete natural density range of polar snow and ice (0.340 to 0.890 g/cm^3). The specimens were loaded rapidly to failure with times varying between 0.2 and 1.4 sec. During loading, head speeds varied between 5.1 and 23.6 cm/min, although during individual tests they were constant. Even the low density specimens failed in the brittle mode. Although a plot of [Sigma]T vs [Gamma] is linear, [Sigma]c vs [Gamma] is clearly nonlinear. This nonlinearity may result from either changes in the level of the internal stress concentrations associated with the voids in the snow or from changes in the ratio (bulk porosity/effective porosity of the failure surface) with density. Both tangent and secant moduli are linear functions of [Gamma]. There is no pronounced change in [Sigma]c with changes in strain rate. A significant increase in [Sigma]T, [Sigma]c and the modulus values was noted at bulk densities greater than 0.830 g/cm^3. This increase is presumably caused by the close-off of the air passages.
    Note: MAB0014.001: ZSP-202-276 , Online frei verfügbar
    In: Research report
    Language: English
    Keywords: Forschungsbericht
    URL: http://www.worldcat.org/oclc/5974547
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